UVic research challenges modern tectonic theory
Some 250-million-years ago, our planet was a very different place indeed, with the continents we know today clustered together in one large supercontinent known as Pangea. But what processes were involved in the construction of Earth’s most recent and renowned supercontinent? A new study led by recent PhD grad, Jessica Shaw, raises some questions about the geological processes involved and challenges a major tenant of modern plate tectonic theory.
Across Spain and Portugal, the ancient Variscan mountain belt of Western Europe bends back on itself in a tight S-shape. Most earth scientists agree this mountain belt was constructed through the continental collisions that formed Pangea. “A fundamental assumption of plate tectonic theory is that tectonic plates are internally rigid and deform only at their margins – where, for example, they collide to create mountain belts ,” says Shaw.
By analyzing hundreds of small folds within rocks of NW Spain, Shaw and her colleagues provide evidence suggesting that the Variscan mountain belt was once linear, and was shortened lengthwise into its modern S-shape after its initial construction.
“Essentially, this means that the tectonic plate containing the Variscan had to deform internally for the mountain belt to reach its current geometry, which would be difficult to achieve at the core of a supercontinent,” says Shaw. “Though there are many outstanding questions regarding the mechanisms of such a process, our findings challenge both the long-standing models for Pangea formation, and the assumption that all tectonic plates are internally rigid.”
The data imply that construction of the Variscan mountain belt may have predated Pangea, and that the true record of supercontinent formation may be the subsequent deformation of the Variscan itself. The continuing research of Shaw and her colleagues is exploring this possibility.
The study was published this August online in Lithosphere, a journal of the Geological Society of America.